1. Field of the Invention
The present invention relates to an imprint apparatus, an imprint method, and a method of manufacturing an article.
2. Description of the Related Art
The imprint technique can transfer a nanoscale fine pattern, and is known as a nanolithography technique for volume production of semiconductor devices and magnetic storage media. An imprint apparatus which employs the imprint technique cures a resin (imprint material) on a substrate while a mold (original) having a pattern formed on it is pressed against the resin to transfer the pattern onto the substrate, as disclosed in Japanese Patent No. 4185941.
In the photo-curing method as one method of curing the resin on the substrate, an ultraviolet-curing resin is irradiated with ultraviolet light while a transparent mold is kept in contact with the resin to cure the resin, and the mold is separated (released) from the cured resin. The photo-curing method is suitable for manufacturing a semiconductor device and a magnetic storage medium because, for example, the temperature can be controlled relatively easily, and an alignment mark formed on the substrate can be detected through the transparent mold.
Also, an imprint apparatus generally adopts the die-by-die alignment scheme as a scheme of alignment between a substrate and a mold. In the die-by-die alignment scheme, for each of a plurality of shot regions on the substrate, an alignment mark formed in the shot region on the substrate is optically detected to correct a shift in positional relationship between the mold and the substrate.
However, in an imprint apparatus, a mold is kept in contact with a substrate through a resin. Therefore, in, for example, pressing the mold against the resin on the substrate, a force acts not only in the direction (perpendicular direction) in which the mold is pressed, but also in the horizontal direction (the direction in which the position of the mold is shifted) perpendicular to the pressing direction. Also, disturbance vibration acts on the mold and the substrate from a structure which holds the mold, and that which holds the substrate, respectively. As a result, the mold is pressed while the positional relationship between the mold and the substrate has changed, that is, pressed at a position shifted from a predetermined position. In other words, even when the mold and substrate are aligned with high accuracy before the mold is pressed against the resin on the substrate, the mold and substrate do not always have a predetermined positional relationship while the mold is pressed. Also, after the mold is pressed against the resin on the substrate, a resin (thin film resin) with tribological properties, that is, a so-called frictional force acts between the mold and the substrate, and this makes it difficult to finely adjust the relative position between the mold and the substrate.
In an imprint apparatus, to improve the pattern transfer accuracy (resolution) while suppressing in-plane variations between shot regions, it is necessary to minimize the film thickness of the resin on the substrate. Also, to shorten the time to fill the mold with the resin, and reduce the force (release force) required to release the mold, a cavity (air chamber) is formed at the central portion of the back surface of the mold (its surface opposite to the pattern surface) to be thinner than the peripheral portion of this surface. Moreover, a soft member is provided on a mold holding unit (holding surface), which holds the mold, along the tilt of the substrate. In this manner, a mold and mold holding unit used in an imprint apparatus are prone to deformation in reaction to an external force. Therefore, the mold and mold holding unit deform due, for example, to the frictional force of the resin on the substrate, and this makes it difficult to align the mold and the substrate with high accuracy (especially, align them in the horizontal direction perpendicular to the pressing direction).